This invention relates to current regulator circuits, particularly those implemented in watch or similar systems operating under limited energy sources e.g., batteries, and designed in the bipolar technologies as for example, integrated injection logic (I.sup.2 L).
In such systems, the limited energy source demands that all circuit functions inherently dissipate minimal power in all operational modes. Electronic watch systems are frequently designed with circuitry that is operated intermittently, such as for setting the time or displaying data etc., or circuitry that is continuously operable except for short periods when some "housekeeping" function is performed at which time the circuitry is inactivated. Circuits of these types fabricated in current controlled logic can be activated or inactivated by a switchable current regulator of the type to be described herein. It is highly desirable that the current regulator dissipate very low power in either the active or inactive state.
The ability to maintain accurate timekeeping is predicated on stable device operation, a part of which is stable current control with varying supply levels. The circuits typically must function over a supply voltage range of 1.0 to 1.6 volts.
Frequently, such watch circuits require a number of independent current sources at separate current levels to energize the several subelements of the watch circuitry. A current regulator capable of such operations is formed around a first transistor and a first collector load means, having substantial direct current impedance, to form a common-emitter or CE amplifier. A second transistor with its base and emitter electrodes respectively connected to the collector and base electrodes of said first transistor provides closed loop feedback around the CE amplifier by means of emitter follower action. The feedback conditions the CE amplifier to regulate the potential between the emitter electrode of the second transistor, which point is also the input to the CE amplifier, and a point of reference potential to which the emitter electrode of the first transistor also returns. This in turn regulates the current that the emitter of the second transistor must supply to a first resistor means connected between the emitter of the second transistor and the point of reference potential to support the regulated potential. The second transistor may be formed with one or more collector electrodes proportioned one to the other to provide output currents related to its emitter current in the same proportions when connected to subsequent circuitry. The collector current of the second transistor may be increased or decreased by quantum steps, as known by the inclusion of forward biased pn junctions in series with the emitter electrode of the first transistor or in series with the first resistive means respectively.
Substantially larger output currents than those supplied from the second transistor may be obtained by applying the regulated potential at the base of the first transistor to bias the base electrodes of one or more transistors having base-emitter junction areas substantially larger than the first transistor, whose emitters are connected to the point of reference potential through current limiting resistive means, and whose collectors are connected to circuits for utilizing said output currents.
Greater insight into the operation of such current regulators may be obtained from U.S. Pat. No. 3,430,155 entitled "Integrated Circuit Biasing Arrangement for Supplying V.sub.BE Bias Voltages" issued Feb. 25, 1969 to L. A. Harwood and U.S. Pat. No. 3,320,439 entitled "Low Value Current Source for Integrated Circuits," issued May 16, 1967 to R. J. Widlar. Transistor structures having more than one collector electrode are described in U.S. Pat. No. 3,579,059 entitled "Multiple Collector Lateral Transistor Device" issued May 18, 1971 to R. J. Widlar.